The login field of the user in Clarity PPM is the one configured as the "User Name".
If this needs to be modified, it can be done via the UI.
- Go to Administration => Resources.
- Select one user for which you would like to do the changes (a test user).
- The properties will display the list of attributes for the resource.
- Modify the "User Name", from its current value to the email of the user.
- Now, the login of the user will be the corresponding configured email address on its "User Name".